Spin-gap physics, ground state degeneracy, and bound states on the depleted kagome lattice

TL;DR

This paper investigates the spin-1/2 Heisenberg model on a depleted kagome lattice, revealing how local and propagating excitations influence ground state degeneracy and bound states in a system with reduced bonds.

Contribution

It introduces a detailed analysis of low-energy excitations and bound states in a depleted kagome lattice, highlighting the role of localised and itinerant modes in ground state properties.

Findings

Localised and itinerant low-energy excitations identified.

Ground state degeneracy remains at finite J_2/J_1 << 1.

Propagating bound states dominate low-energy excitations.

Abstract

We analyse the antiferromagnetic spin-1/2 Heisenberg model on a depleted kagome lattice, where some bonds have been reduced to exchange integral J_2 << J_1. The fully depleted system consists of 1D chains, each with a doubly degenerate singlet-pair ground state and a spectral gap (like the Majumdar-Ghosh model). There are localised and itinerant low-energy excitations. The modes from the lowest branch of excitations are incapable of lifting the 2D system's ground state degeneracy at finite J_2/J_1 << 1. Low-energy excitations of the 2D system are dominated by coherently propagating bound states of the 1D excitations.